Micro-fabrication involves the fabrication of very small structures, for example, and without limitation, structures having features on the order of micro-meters or smaller. One area in which micro-fabrication has had a sizeable impact is in processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, micro-fabrication becomes increasingly important since micro-fabrication provides greater process control while allowing a reduction in the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication have been employed include biotechnology, optical technology, mechanical systems and the like.
An exemplary micro-fabrication technique is disclosed in U.S. Pat. No. 6,334,960 to Willson et al. In particular, the Willson et al. patent discloses a method of imprint lithography to form a relief pattern in a structure. The method includes providing a substrate having a transfer layer (typically spin-coated), and covering the transfer layer, in turn, with a low viscosity, polymerizable (typically UV curable) fluid composition (typically in the form of droplets). The method further includes mechanically contacting an imprint template or mold having a relief structure with the polymerizable fluid composition wherein the polymerizable fluid composition fills a gap between the imprint template and the substrate and fills the relief structure of the imprint template. Next, the method includes subjecting the polymerizable fluid composition to conditions to solidify and to polymerize the same (typically, exposing the polymerizable fluid composition to UV to crosslink it), thereby forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the imprint template. Next, the method includes separating the imprint template from the substrate to leave solid polymeric material on the substrate, which solid polymeric material includes a relief pattern in the form of the complimentary relief structure. Next, the solidified polymeric material and the transfer layer are subjected to an environment to selectively etch the transfer layer relative to the solidified polymeric material to form a relief image in the transfer layer.
The following issues that relate to selective adhesion of the solidified polymeric material to different surfaces are typically considered when one develops a method and/or a material useful in forming fine-feature relief patterns in the solidified polymeric material. First, the solidified polymeric material ought to adhere well to the transfer layer on the substrate, and second, it ought to be easily released from the surface of the imprint template. These issues are typically referred to as release characteristics, and if they are satisfied, the relief pattern recorded in the solidified polymeric material will not be distorted during separation of the imprint template from the substrate.
In addition to the above-described release characteristics, when designing an imprinting material for use in imprint lithography, further considerations include: (a) low viscosity, for example, and without limitation, a viscosity, at 25° C., of 5 centipoise or less, to fast spread over both the substrate and the surface of the imprint template, and to fast fill the imprinting material into the relief pattern. It is better if the viscosity is sufficiently low so that minimal pressure, for example, and without limitation, a pressure of about 2-4 psi, and no additional heating are necessary to move the imprinting material into the relief pattern on the imprint template; (b) low vapor pressure so that there is little evaporation (evaporation is a problem since the droplets of imprinting material may be on the order of 80 pico-liters, and this results in droplets having a large ratio between surface area and volume); and (c) cohesive strength of the cured imprinting material.
In light of the above, there is a need for imprinting materials for use in imprint lithography that satisfy one or more of the above-identified design criteria.